Quantitative analysis of smooth endoplasmic reticulum proliferation in periportal, midzonal and perivenular hepatocytes of mice after administration of phenobarbital.

Smooth endoplasmic reticulum (SER) proliferation after phenobarbital (PB) administration has been described to occur predominantly in perivenular hepatocytes. We analyzed by quantitative electron microscopy changes in ER amounts in periportal, midzonal and perivenular hepatocytes from mice injected with 35, 50, 100 or 150 mg/kg of PB once a day for 3 days. The SER proliferated in midzonal hepatocytes in addition to perivenular hepatocytes even when low doses (35 or 50 mg/kg) were administered, and in hepatocytes of all three zones in case of high doses (100 or 150 mg/kg). Moreover, net proliferation of SER after administration of an amount of PB was not different in hepatocytes of any zones where the proliferation occurred, except animals injected with 100 mg/kg. The results suggest that there is no difference in SER producing capacity in hepatocytes of three zones when the cells have recognized the stimulation of PB.